Guidelines for Using Perchloric Acid
Perchloric acid (HClO4) is a strong mineral acid. Under some circumstances it may act as an
oxidizer and/or present an explosion hazards. These guidelines present information on how to
handle and store perchloric acid safely. Please notify EH&S at 8-8182 if you are using perchloric
acid in your laboratory.
Using Perchloric Acid (< 72%) at Room Temperature
At room temperature, perchloric acid up to concentrations of 72% has properties similar to other
strong mineral acids. It is a highly corrosive substance and causes severe burns on contact with
the eyes, skin, and mucous membranes. When used under these conditions, perchloric acid reacts
as a strong non-oxidizing acid. The following precautions should be taken when using perchloric
acid under these conditions:
· Substitute with less hazardous chemicals when appropriate. Use dilute solutions (< 60%)
whenever possible.
· Conduct operations involving cold perchloric acid in a properly functioning chemical fume
hood with current EH&S certification. If operations are conducted frequently or in large
quantities contact EH&S to determine if a specially designed fume hood dedicated to perchloric
acid use is required.
· Always use impact-resistant chemical goggles, a face shield, neoprene gloves, and a rubber
apron when handling perchloric acid.
· When using or storing even dilute perchloric acid solutions avoid contact with strong
dehydrating agents (concentrated sulfuric acid, anhydrous phosphorous pentoxide, etc.). These
chemicals may concentrate the perchloric acid and make it unstable.
· Always transfer perchloric acid over a sink or other suitable containment in order to catch any
spills and afford a ready means of cleanup and disposal.
· Perform all operations on chemically resistant surfaces. Avoid contact with cellulose materials
such as wood, paper and cotton. Perchloric acid may become concentrated and cause a fire or
explosion.
Using Heated Perchloric Acid (<72%)
When heated to temperatures above 150° C perchloric acid becomes a strong oxidizer and
eventually becomes unstable. Concentrated solutions are very dangerous and can react violently
with many oxidizable substances, such as paper and wood, and can detonate. Vapors may also
contaminate work surfaces or ventilation equipment with perchlorate residues, which may form
highly unstable compounds, such as metallic perchlorates. These compounds may ignite or
detonate under certain conditions. The following additional precautions should be followed when
heating perchloric acid:
· Perchloric acid digestions and other procedures performed at elevated temperatures should be
done in a specially designed perchloric acid fume hoods. Contact EH&S to schedule use.
If procedures involving heated perchloric acid are performed only rarely other accepted methods
to capture and contain vapors may be used in place of a perchloric acid hood. If you have been
performing perchloric acid digestions in a fume hood not designed for perchloric acid, contact
EH&S immediately for an evaluation of perchlorate contamination of the hood.
· Lower the fume hood sash as much as possible so that it can function as a physical barrier or
use a safety shield to provide splash/splinter protection. Perchloric acid fume hoods should have
shatterproof glass.
· Never heat perchloric acid in an oil bath or with an open flame. Electric hot plates, electrically
or steam-heated sand baths, heating mantles, or steam baths are preferred. Use explosion proof
electrical equipment.
· Avoid allowing hot perchloric acid to come into contact with any organic materials, including
paper or wood, because a fire or explosion can occur. Avoid storing these materials in perchloric
acid work hoods. Avoid using greases or hoses that are incompatible with perchloric acid.
· Be sure you understand the reaction(s) that can occur when using perchloric acid. Perchloric
acid may react violently with many chemicals, including acetic anhydride, alcohol, reducing
agents, and many metals.
· In wet digestions with perchloric acid, treat the sample first with nitric acid to destroy easily
oxidizable matter.
· Do not distill perchloric acid in a vacuum, because the unstable anhydride may be formed and
cause a spontaneous explosion. Protect vacuum sources from perchloric acid/perchlorate
contamination. Vacuum pumps should be thoroughly flushed and refilled with Kel-F or
Fluorolube.
· Wash down perchloric acid hoods after each use, following operating instructions provided by
the manufacturer of the perchloric acid hood.
· If an apparatus cracks or breaks due to thermal or mechanical shock, the hazards are sufficient
to make it desirable to consider using quartz apparatus since it is necessary in many experiments
to chill perchloric acid rapidly from the boiling point. Glass-to-glass unions, lubricated with 72%
perchloric acid, seal well and prevent joint freezing arising from the use of silicon lubricants.
Rubber stoppers, tubes, or stopcocks are incompatible with perchloric acid.
· When handling beakers of hot acid use properly designed tongs or other remote-handling
devices.
Using Anhydrous Perchloric Acid
Anhydrous perchloric acid (> 85% concentration) is very unstable and will usually explode when
it comes in contact with organic materials. Follow these additional precautions when working
with anhydrous perchloric acid.
· Allow only experienced research workers to handle anhydrous perchloric acid. These workers
shall be thoroughly familiar with the literature on the acid. Assure that a second worker is
informed of the intended use of the anhydrous perchloric acid. This second worker should be in
sound or sight contact with the worker using anhydrous perchloric acid.
· Use a safety shield to protect oneself against the effects of a possible explosion.
· Use the acid in a designated, properly designed perchloric acid hood with a minimum of
equipment present. No extraneous chemicals should be present in the hood.
· Use thick gauntlets in addition to PPE previously recommended.
· Use only freshly prepared acid. Do not make any more anhydrous perchloric acid than is
required for a day/shift.
Perchloric Acid Spills
CLEAN UP SPILLS OF PERCHLORIC ACID ONLY IF YOU HAVE BEEN TRAINED
TO DO SO AND THE APPROPRIATE EQUIPMENT IS AVAILABLE! If you need
assistance, call EH&S. To clean a spill, neutralize it with soda ash (sodium carbonate) or other
appropriate neutralizing agent. Soak up the neutralized spill with an inorganic based absorbent, if
possible. If rags, paper towels are used, wet them and place them in a plastic bag and seal it. Do
NOT use rags, paper towels, or sawdust and then put them aside to dry out, as such materials
may spontaneously ignite. A second neutralization and rinsing of the wetted area is
recommended. Label waste as flammable hazardous waste and submit an On-line Request for
Hazardous Waste Pickup (www.cmu.edu/ehs).
Storage
The quantities of perchloric acid kept in storage should be kept to a minimum. Perchloric acid
should be stored in its original container within compatible secondary containment, preferably
glass or porcelain. Glass trays should be wiped periodically. It should be separate from other
chemicals, but may be stored with other inorganic acids, preferably in a metal cabinet designed
for acid/corrosive storage. It may also be stored in a perchloric acid fume hood. Perchloric acid
must be stored away from organic chemicals, flammable or combustible materials and strong
dehydrating agents such as sulfuric acid and anhydrous phosphorus pentoxide.
If a bottle containing perchloric acid has turned dark and has crystals forming around the bottom
of the bottle, there is a potential explosion hazard. Do NOT move the bottle, but contact EH&S
for immediate assistance.
Inappropriate and Appropriate Materials
· The following materials are not recommended for use with 72% perchloric acid:
Nylon/polyamides, Dynel/modacrylic ester, Dacron/polyester, Bakelite, Lucite, vegetable-based
Micarta, cellulose-based lacquers, copper/brass/bronze (which form shock sensitive salts),
aluminum (dissolves), high nickel alloys (dissolve), cotton, wool, wood, and litharge (glycerin
and lead oxide).
· The following are suitable for use with 72% perchloric acid: Viton, tantalum, chemically pure
titanium, zirconium, niobium, Hastelloy C (slight corrosion rate), PVC, Teflon, polyethylene,
polypropylene, Kel-F, vinylidene fluoride, Saran, epoxy resins, glass, glass-lined steel, alumina,
and Fluorolube.
Surface Contamination Tests for Perchlorates
· Diphenylamine Test: Dissolve one gram of diphenylamine in 10 ml of "1 to 1" (18 normal)
sulfuric acid to form a diphenylamine sulfate solution. Using a medicine dropper apply this
solution to the test surface. The liquid turns black upon contact with perchlorate. The solution
also reacts with nitrates, but turns blue.
· Methylene Blue Test: Use 0.4% solution of methylene blue in water. Add a few drops of
indicator solution to about 25 ml of trial solution, such as water used to test rinse from a length
of potentially contaminated duct. Perchlorates will produce a violet precipitate.
1. Most of the information for this document was taken from Lawrence Livermore National
Laboratory's ES&H Manual, Chapter 14.8 Working Safely with Corrosive Chemicals. Additional
information is included from; CRC Handbook of Laboratory Safety, NFPA 45 Fire Protection for
Laboratories Using Chemicals, and fact sheets from the University of Ottawa, University of
Illinois at Urbana Champaign, University of California at San Francisco and the Oklahoma
Medical Research Foundation.